Soil Organic Carbon Fractions and Stocks as Affected by Organic Fertilizers in Rice Paddy Soil

Abstract

This research evaluated the effect of different organic fertilization (OF) on soil organic carbon (SOC) stock and fractions in rice paddy soil. The OF system consisted with NPK, NPK+Rice straw (NPK+RS), NPK+Cow compost (NPK+CC), NPK+Swine compost (NPK+SC) and no-fertilization (Control). Labile organic C fractions and humification rates were characterized and SOC stock was determined with bulk density and SOC content. Application of OF significantly SOC content by 7-12% and 23-33% over the NPK and control, while it decreased bulk density by 2-6% and 11-14%. The lowest bulk density was found in RS, which indicated the improvement of soil physical property. The highest SOC stock (38-39 kg C ha-1) was observed in SC and CC treatments. The SOC stock showed significant negative correlation with bulk density (p < 0.001), and positively correlated with humification rate, grain yield (p < 0.01) and HWEC and straw yield (p < 0.05), indicating key roles of SOC on soil quality. These results showed that the OF application largely increased SOC stocks, rice yield, and concentration of labile C and stable C. Therefore, application of OF is recommendable for suitable soil management strategy to improve soil fertility and increase crop yield in rice paddy field. Correlation analysis between soil organic carbon fractions under different fertilization system. Parameter SOC† Bulk density HA FA HA/FA§ HR¶ HA/SOM∮ FA/SOM∮ WEC∫ HWEC∫ Grain Straw SOC stock 1 B. density - < 0.001***† 1 HA 0.103 0.070 1 FA 0.013* 0.027* 0.008** 1 HA/FA 0.754 0.512 < 0.001*** 0.801 1 HR 0.008 - 0.010** < 0.001*** < 0.001*** 0.021* 1 HA/SOM 0.032* - 0.026* < 0.001*** 0.004** 0.001*** 0.001*** 1 FA/SOM 0.001*** - 0.007** 0.009** < 0.001*** 0.787 0.001*** 0.003** 1 WEC < 0.001 - 0.001*** 0.214 0.026* 0.986 0.035* 0.099 0.006** 1 HWEC 0.047* - 0.039* 0.431 0.045* 0.680 0.153 0.310 0.030* 0.07 1 Grain 0.011* - 0.004** 0.157 0.450 0.206 0.105 0.093 0.254 0.10 0.060 1 Straw 0.043* - 0.004** 0.433 0.857 0.360 0.356 0.315 0.586 0.039* 0.207 < 0.001*** 1 †*, **, and *** denote significance at the 5, 1, and 0.1% levels, respectively.†SOC: Soil organic carbon§HA/FA: Ratio of humic acid content and fulvic acid content¶HR: Humification rate∮HA/SOM and FA/SOM: Proportion of humic acid to SOM content and Proportion of fulvic acid to SOM content∫WEC and HWEC: Water extractable carbon and hot water extractable carbon